Polydiacetylenes are polymers of diacetylene monomers, with a backbone structure characterized by the alternate carbon double bond and carbon triple bond therein. When being close enough to each other to form a crystalline or semi-crystalline state, diacetylene monomers undergo polymerization under UV or gamma radiation to afford the conjugated polymers. An aqueous dispersion of polydiacetylene in a suitable condition or a thin film of polydiacetylene on a solid substrate appears blue with a maximum absorbance peak at about 650 nm. Upon exposure to external stimuli (e.g., heat, solvents, pH, molecular recognition, etc.), polydiacetylenes can change in color from blue to red with a maximum absorbance peak at about 550 nm. This characteristic of color transition under specific conditions has recently inspired active research into the use of polydiacetylene as various sensors. As far as polydiacetylene-based sensors are concerned, reference may be made to Korean Patent No. 10-1199417, and Journal of Materials Chemistry, 21, 2648-2655 (2011), which both pertain to polydiacetylene-based polymer sensor fibers, and use thereof in detecting adulterated gasoline. Nowhere has the application of polyacetyelene to fingerprint recognition been mentioned in previous documents.
A fingerprint is an impression left by the friction ridges of a human finger. Fingerprints, the recovery of which from a crime scene is an important method of forensic science, are easily deposited on suitable surfaces by the natural secretions of sweat from the eccrine glands, epocrine glands, and sebaceous glands that are present in epidermal ridges. The secretions are composed mostly of water, together with a minor portion of inorganic materials such as chlorides and metal ions, and organic materials such as amino acids, urea, proteins, carbohydrates, and fatty acids. These secretions are colorless and thus invisible to the naked eye. In the present invention, polydiacetylenes are remarkably improved in chromatic transition and fluorescent change by modifying the diacetylene moieties with alkali metal ionic compounds, thereby being able to highly sense even a trace of water secreted from sweat pores in the friction ridges. When fingers are pressed against the thin film of the present invention, not only do friction ridge patterns appear thereon, but also a distribution of sweat pores in the ridges is distinctively shown, thus visualizing a distribution map of sweat pores. Each person has their own peculiar friction ridge patterns, and is also different from one to another in the distribution of sweat pores in the friction ridges. Thus, even a very small portion of the sweat pore map printed on the thin film can guarantee the intrinsic fingerprint characteristics of the fingerprint provider of interest. As mentioned above, a combination of the fingerprint and the distribution map of sweat pores, obtained according to the present invention can approximate the fingerprint recognition rate to 100%, and can be used to prevent the crime of fingerprint forgery. The present invention is an original technology because it has not been reported thus far.
[Related Art Document] Korean Patent No. 10-1199417.